Yes, I've broken a couple of centerboards. One I shattered hitting an underwater boulder at speed. It is unrepairable, but I keep it as a reminder of hidden dangers. The other sounds like what you have. The hook on the centerboard broke off. That board I repaired by boring a 13/16 dia hole about 4" deep into the end that had the hook and filling the hole about 1/3 full of fiberglass resin and inserting a 5" threaded 3/4" dia fiberglass rod displacing much of the resin till the rod bottoms out (be ready to wipe up the ooze) and let set up. Then wrap exposed rod with resin impregnated fiberglass string (yarn) so that it is over build (larger than what the finished size would be). Then shape with files (round and flat) to match other board. Once in the desired shape is achieved, seal with a thin layer of resin. Paint if you like. The repaired hook has lasted me for 4 years of vigorous sailing (so far).

I had a centerboard break at the hook too (actually, I bought the boat that way knowing I would have to repair it). The problem is that the fiberglass reinforcement doesn't extend all the way around to the end of the hook. Most of the tip of the hook is just gelcoat, so it doesn't have adequate structrual reinforcement. If I recall correctly, I fixed mine by making a rough mold out of masking tape around the tip of the centerboard. Then poured in polyester resin and let it cure. Then filed it to the correct shape and laminated a couple layers of fiberglass cloth around the tip. Once you get some glass around the tip, it should be plenty strong.